What is the function of a roof deck?

• A. The structural base for the roof covering.
• B. An insulation layer inside the attic.
• C. A decorative surface over the roof deck.
• D. A weatherproof membrane applied over the deck.

Answer: (A)

The roof deck is the solid, structural base for the roof covering. It’s the flat, nailable surface—usually plywood or OSB—installed over the rafters or trusses, providing a continuous plane that carries the weight of shingles, tiles, or metal panels and transfers those loads to the framing. It also serves as the substrate for attaching the roofing components, including underlayment and the final roof material. Insulation sits in the attic or between framing, not on the deck, and weatherproofing comes from the underlayment, flashing, and roofing material, not the deck itself. So the deck’s role is to provide a sturdy foundation for the entire roofing system.